This invention relates to an electric motor assisted vehicle and more particularly to an improved torque sensor therefor.
There have been proposed a class of vehicle wherein the vehicle is powered primarily by a manual input force of the operator. However, there is also incorporated an electric motor assist which provides assist power for assisting the operator's manual propulsion of the associated vehicle. Although the type of vehicle employed for this purpose may be of a wide variety, this type of system is frequently used on land vehicles such as bicycles that have a generally open construction.
Specifically, the type of system generally employs a manual force receiving device such as a pedal operated crank mechanism that drives a transmission for driving an output shaft for propelling the vehicle. An electric motor is employed in conjunction with this pedal operated mechanism for providing electric power assist for driving the vehicle. Generally, at least one sensor is also incorporated in this mechanism that senses the input force of the operator to the pedal operated mechanism. This sensed signal is then sent to a controller which, in turn, controls the transmission of electrical power from a battery to the electric motor for determining the amount of electric power assist.
A type of electric power assisted pedal operated vehicle of the type aforedescribed is shown in U.S. Pat. No. 5,570,752 issued Nov. 5, 1996 and assigned to the assignee hereof. As has been noted, in order to provide the requisite power assist, it is desirable to incorporate a torque sensor which will sense the manual input force to the pedal mechanism. In this way, the output force can be related to the input force so as to maintain a normal feel to the rider of the bicycle while still providing the electrical power assist.
It is also desirable to provide a sensor that senses the speed as this is useful in limiting the amount of power assist to those instances where the power assist is required as when climbing hills or accelerating from a standstill. However, it may be desirable to limit the power assist as the speed of the vehicle increases. The positioning and operation of the torque and speed sensors further complicates the overall construction.
A prior art type of torque sensor is shown in FIG. 1 and will be described by reference to that figure to describe certain of the problems attendant with the prior art type of constructions. In this figure, the outer housing of the crank assemblage is indicated generally by the reference numeral 31. Although the internal description of the crank mechanism will not be described in full detail, reference may be had to aforenoted U.S. Pat. No. 5,570,752 for the details of the construction.
Basically, a crankshaft 32 is supported for rotation within the housing 31 and carries pedals at the outer ends of its crank arms for pedal application of force to the crankshaft 32.
A transmission of a step-up type, which may include a planetary gear set, is interposed between the crankshaft 32 and the output shaft that drives a sprocket for driving the rear wheel of an associated bicycle, if this is the type of vehicle application chosen.
This transmission includes a sun gear that is carried for limited pivotal movement by a torque-sensing member 33. This member 33 has an abutment surface 34 that is adapted to engage a sensor mechanism, indicated generally by the reference numeral 35. This sensor mechanism 35 is mounted within a cavity 36 and includes a potentiometer 37. The potentiometer 37 has a shaft 38 on which a sensor arm 39 is affixed.
This sensor arm is urged by a spring assembly, indicated generally by the reference numeral 41, to resist rotation of the torque-sensing member 33. The spring assembly 41 includes a coil compression spring 42 that bears against a plunger 43 which, in turn, acts on the potentiometer arm 39. The spring 42 is loaded by means of a plate 44 and the plunger 43 has its shaft journaled within a support member 45. The degree of rotation of the potentiometer arm 39 will cause rotation of the potentiometer shaft 38 and will provide an output signal indicative of the operator input torque.
It should be readily apparent that this sensor structure requires a fairly substantial amount of space and also results in the mounting of the component in a way that they can be damaged and hence it is necessary to provide a protective plate 46 which further adds to the bulk of the mechanism and limits its space availability.
Furthermore the sliding engagement between the various components and particularly the plunger 43 and the potentiometer arm 39 and the abutment surface 34 and the arm 39 introduce hysteresis into the system. Also the sliding motion between the plunger 43 and the arm 39 can cause wear. Since all forces are taken by the potentiometer shaft 38 its bearing arrangement must be robust and hence expensive.
It is, therefore, a still further object of this invention to provide an improved sensor assembly for use with an electric power-assisted pedal operated vehicle drive mechanism.